Batteries have limited life spans. When the charge is depleted in a battery, the battery-powered device will cease to function. To circumvent loss of functionality, the battery must be replaced or recharged prior to charge depletion. Accurate determination of a battery's state of depletion is particularly important for battery-powered medical devices that are implanted in human patients. With an accurate determination of battery depletion state, an implanted medical device may be recharged or replaced in order to maintain monitoring and/or therapy.
Pulse generators (PGs) are battery-powered medical devices that are implanted in patients and provide electrical pulses (therapy) to stimulate or shock the patient's heart. PGs include cardiac rhythm management (CRM) devices, such as pacemakers, heart failure devices, and defibrillators. One or more remote sensors may be under the control of the PG to provide information that may be used to determine whether to administer therapy to the patient. A battery may serve as the power source in each of the sensors, providing power to, for example, measure physiological parameters and transmit data related to the measured parameters via telemetry. Accurate determination of a battery charge of a remote device supports an effective assessment of the appropriate replacement or recharge time.